Inside inflation: after the big bang

By Peter Coles

MASSACHUSETTS, 1981. A young physicist comes up with what seems to be an absurd idea&colon; the universe went through a period of ultra-fast expansion just after the big bang. Alan Guth cannot prove that this “inflation” actually happened nor can he suggest a compelling physical reason why it should have, but the idea seems nevertheless to solve several major problems in cosmology.

Fast forward to today. Guth is a professor at the Massachusetts Institute of Technology and inflation is now well established as an essential component of cosmology. But should it be?

There is little direct evidence that inflation actually took place. Observations of the cosmic microwave background – “fossil” radiation from the big bang – are consistent with the idea that inflation took place, but that doesn’t mean it actually happened. What’s more, we still don’t know what would have caused it if it did. So how confident can we be that inflation is really a part of the universe’s history?

A quarter of a century ago, our understanding of the universe was much less precise than it is today. In those days it was a domain in which theoretical speculation ruled over measurement and observation. Technology simply wasn’t up to the task of performing large-scale galaxy surveys or detecting the all-important details in the cosmic microwave background (see “Shadow of the big bang”).

14 billion light years size of the observable universe today

The lack of stringent experimental constraints made cosmology a theorists’ paradise in which many imaginative and esoteric ideas blossomed. Not all survived to be included in the standard model of cosmology, but inflation has proved to ...

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